Exit Zen
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../../exercises/sockets.rst:330
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send the most significant byte followed by the least significant byte
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../../principles/network.rst:147
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The first technique assumes that the underlying network topology is a tree. A tree is the simplest network to be considered when forwarding packets. The main advantage of using a tree is that there is only one path between any pair of nodes inside the network. Since a tree does not contain any cycle, it is impossible to have forwarding loops in a tree-shaped network.
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../../principles/reliability.rst:188
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The datalink layer
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../../principles/sharing.rst:182
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`Which packet(s) should be discarded ?` Once the network node has decided to discard packets, it needs to actually discard real packets.
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../../principles/transport.rst:89
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send the least significant byte followed by the most significant byte
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../../bibliography.rst:133
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Mills, D.L., `Computer Network Time Synchronization: the Network Time Protocol <http://books.google.com/books?id=pdTcJBfnbq8C>`_. CRC Press, March 2006, 304 pp.
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../../glossary.rst:321
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A service that enables a user to send or receive a file from a distant server over the network. The File Transfer Protocol :term:`FTP` was a popular service. It has now been replaced by HTTP/HTTPs or more secure protocols such as the `SSH File Transfer Protocol <https://en.wikipedia.org/wiki/SSH_File_Transfer_Protocol>`_.
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../../exercises/network.rst:360
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Routes on E
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../../exercises/sockets.rst:331
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send the least significant byte followed by the most significant byte
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../../principles/network.rst:151
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In a tree-shaped network, it is relatively simple for each node to automatically compute its forwarding table by inspecting the packets that it receives. For this, each node uses the source and destination addresses present inside each packet. Thanks to the source address, a node can learn the location of the different sources inside the network. Each source has a unique address. When a node receives a packet over a given interface, it learns that the source (address) of this packet is reachable via this interface. The node maintains a data structure that maps each known source address to an incoming interface. This data structure is often called the `port-address table` since it indicates the interface (or port) to reach a given address.
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../../principles/sharing.rst:185
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By combining different answers to these questions, network researchers have developed different packet discard mechanisms.
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../../principles/transport.rst:91
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The first possibility was named `big-endian` in a note written by Cohen [Cohen1980]_ while the second was named `little-endian`. Vendors of CPUs that used `big-endian` in memory insisted on using `big-endian` encoding in networked applications while vendors of CPUs that used `little-endian` recommended the opposite. Several studies were written on the relative merits of each type of encoding, but the discussion became almost a religious issue [Cohen1980]_. Eventually, the Internet chose the `big-endian` encoding, i.e. multi-byte fields are always transmitted by sending the most significant byte first, :rfc:`791` refers to this encoding as the :term:`network-byte order`. Most libraries [#fhtonl]_ used to write networked applications contain functions to convert multi-byte fields from memory to the network byte order and the reverse.
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../../bibliography.rst:147
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Rago, S., `UNIX System V network programming <http://www.pearsonhighered.com/educator/product/UNIX-System-V-Network-Programming/9780201563184.page>`_, Addison Wesley, 1993
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../../glossary.rst:63
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frame
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../../exercises/network.rst:363
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A
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../../principles/network.rst:153
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Learning the location of the sources is not sufficient, nodes also need to forward packets towards their destination. When a node receives a packet whose destination address is already present inside its port-address table, it simply forwards the packet on the interface listed in the port-address table. In this case, the packet will follow the port-address table entries in the downstream nodes and will reach the destination. If the destination address is not included in the port-address table, the node simply forwards the packet on all its interfaces, except the interface from which the packet was received. Forwarding a packet over all interfaces is usually called `broadcasting` in the terminology of computer networks. Sending the packet over all interfaces except one is a costly operation since the packet is sent over links that do not reach the destination. Given the tree-shape of the network, the packet will explore all downstream branches of the tree and will finally reach its destination. In practice, the `broadcasting` operation does not occur too often and its performance impact remains limited.
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../../principles/referencemodels.rst:152
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the `Application layer` that contains the mechanisms that do not fit in neither the Presentation nor the Session layer. The OSI Application layer was itself further divided in several generic service elements.
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../../principles/reliability.rst:194
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To enable the transmission/reception of frames, the first problem to be solved is how to encode a frame as a sequence of bits, so that the receiver can easily recover the received frame despite the limitations of the physical layer.
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../../principles/transport.rst:93
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Besides 16 and 32 bit words, some applications need to exchange data structures containing bit fields of various lengths. For example, a message may be composed of a 16 bits field followed by eight, one bit flags, a 24 bits field and two 8 bits bytes. Internet protocol specifications will define such a message by using a representation such as the one below. In this representation, each line corresponds to 32 bits and the vertical lines are used to delineate fields. The numbers above the lines indicate the bit positions in the 32-bits word, with the high order bit at position `0`.
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../../bibliography.rst:308
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Ramakrishnan, K. K. and Jain, R., `A binary feedback scheme for congestion avoidance in computer networks with a connectionless network layer <http://doi.acm.org/10.1145/205447.205461>`_. SIGCOMM Computer Communication Review 25, 1 (Jan. 1995), 138-156.
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